"Using a Mac may certainly be a safer choice for a lot of people as despite being vulnerable they are not targeted. However this is not the same as Macs being secure, something Eric Schmidt erroneously advised recently. I may be able to browse impervious to malware on a Mac at the moment, however I personally would not be comfortable using a platform so easily compromised if someone had the motivation to do so. In this article I address just why OS X is so insecure including the technical shortcomings of OS X as well as Apples policies as a company that contribute to the situation."

- Worm.OSX.Tored.A (Worm that propegated through Mac network shares and through Apple Mail).

Those are three that I am aware of without even looking very hard. None of them achieved very wide spread infections because they could only propegate through Macs. And since Macs were not very popular yet when they were creagted, many infected Macs searched in vain trying to find another Mac that they could infect.

"Those are three that I am aware of without even looking very hard. None of them achieved very wide spread infections because they could only propegate through Macs."

I always thought that the argument was (simply) that macs were less of a target for malware authors due to small market share.

However it never occurred to me to think that even when the mac os is targeted by viruses, those viruses will have more trouble than windows viruses in randomly finding more targets. The lack of targets would help retard mac virus propagation.